# NestJS Search & CQRS

> Elasticsearch integration and Sync patterns.

- Skill: `majiayu000/nestjs-search-cqrs` (Agent Skill, multi-file: 2 files)
- Install (CLI): `npx skillmds add majiayu000/nestjs-search-cqrs`
- Raw SKILL.md: https://api.skillmd.com/api/skills/majiayu000/nestjs-search-cqrs/raw
- Safety review: pending
- Works with: Claude Code, Claude.ai, OpenAI Codex
- Category: Integrations & APIs
- Author: majiayu000 (https://skillmd.com/u/majiayu000)
- Updated: 2026-09-09
- Page: https://skillmd.com/skills/majiayu000/nestjs-search-cqrs

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# Search Engine & Full-Text

## **Priority: P1 (OPERATIONAL)**

Full-text search implementation with Elasticsearch and database patterns.

- **Pattern**: **CQRS (Command Query Responsibility Segregation)**.
  - **Write**: To Primary Database (Postgres/MySQL). Source of Truth.
  - **Read (Complex)**: To Search Engine (Elasticsearch, OpenSearch, MeiliSearch). Optimized for filtering, fuzzy search, and aggregation.

## Synchronization (The Hard Part)

- **Dual Write (Anti-Pattern)**: `await db.save(); await es.index();`.
  - _Why_: Partial failures leave data inconsistent. Slows down HTTP response.
- **Event-Driven (Recommended)**:
  1. Service writes to DB.
  2. Service emits `EntityUpdated`.
  3. Event Handler (Async) pushes to Queue (BullMQ).
  4. Worker indexes document to Search Engine with retries.
- **CDC (Golden Standard)**: Change Data Capture (Debezium). Connects directly to DB transaction log. No app conceptual overhead, but higher ops complexity.

## Organization

- **Module**: Encapsulate the client in a `SearchModule`.
- **Abstraction**: Create generic `SearchService<T>` helpers.
  - `indexDocument(id, body)`
  - `search(query, filters)`
- **Mapping**: Use `class-transformer` to map Entities to "Search Documents". Search docs should be flatter than Relational entities constraints.

## Testing

- **E2E**: Do not mock the search engine in critical E2E flows.
- **Docker**: Spin up `elasticsearch:8` container in the test harness to verify indexing works.